Batterjee Medical College. Haemophilus influenzae Diseases Sinusitis, otitis media & pneumonia are...

Batterjee Medical College


Haemophilus influenzae

Diseases• Sinusitis, otitis media & pneumonia are common.• Epiglottitis is uncommon.• H. influenzae used to be a leading cause of

meningitis, but vaccine has greatly reduced number of cases.



Characteristics

Habitat and Transmission

•Small gram-negative (coccobacillary) rods.•Requires factors X (hemin) & V (NAD) for growth.•Of six capsular polysaccharide types, type b causes 95% of invasive disease. •Type b capsule is polyribitol phosphate.

•Habitat is the upper respiratory tract.

•Transmission is via respiratory droplets.


Pathogenesis


• Polysaccharide capsule is the most important

determinant of virulence.• Unencapsulated ("untypeable") strains cause

mucosal infections but not invasive infections. • IgA protease is produced. • Most cases of meningitis occur in children younger

than 2 years of age, because maternal antibody has

waned & immune response of child to capsular

polysaccharides can be inadequate.


Laboratory Diagnosis


•Gram-stained smear plus culture on chocolate agar.•Growth requires both factors X & V. •Determine serotype by using antiserum in various tests, e.g., latex agglutination.•Capsular antigen can be detected in serum or cerebrospinal fluid.


Treatment


•Ceftriaxone is the treatment of choice for meningitis.•Approximately 25% of strains produce β -lactamase.

• Vaccine containing type b capsular polysaccharide conjugated to diphtheria toxoid or other protein is given between 2 & 18 months of age.• Rifampin can prevent meningitis

in close contacts.

Prevention


Bordetella pertussis

Diseases

Whooping cough (pertussis).

Characteristics

Small gram-negative rods.


• Habitat is the human respiratory tract.• Transmission is via respiratory

droplets.


Pathogenesis


• Pertussis toxin stimulates adenylate cyclase by adding ADP-ribose onto inhibitory G protein.

• Toxin has two components: - Subunit A: has ADP-ribosylating activity - Subunit B:binds toxin to cell surface receptors.

• Pertussis toxin causes lymphocytosis in blood by inhibiting chemokine receptors prevents lymphocytes from entering tissue, resulting in large numbers being retained in blood.


Pathogenesis


• Inhibition of chemokine receptors occurs because

pertussis toxin ADP-ribosylates inhibitory G

protein prevents signal transduction within cell

• Extracellular adenylate cyclase is produced

inhibit killing by phagocytes.

• Tracheal cytotoxin damages ciliated epithelium of

respiratory tract.


Bordetella pertussis •Whooping cough is acute tracheobronchitis that begins with mild upper respiratory tract symptoms followed by severe paroxysmal cough, which lasts from 1 to 4 weeks.•Paroxysmal pattern is characterized by series of hacking coughs, accompanied by production of copious amounts of mucus, that end with inspiratory "whoop" as air rushes past narrowed glottis.

•In adults, B. pertussis infection often manifests as paroxysmal cough of varying severity lasting weeks. The characteristic whoop is often absent. Adults with a cough lasting several weeks (often called the 100-day cough) should be evaluated for infection with B. pertussis.




•Gram-stained smear plus culture on Bordet-Gengou agar. • Identified by biochemical reactions & slide agglutination with known antisera.• PCR tests are both sensitive & specific.

Colonies of Bordetella pertussis growing on Bordet-Gengou agar This fastidious bacterium grows as small colonies with a pearl-like sheen on this medium.


Treatment


Erythromycin.

Prevention

•Acellular vaccine containing pertussis toxoid &

four purified proteins (recommended).

•Killed vaccine: contains whole organisms.

•Given to children in combination with diphtheria &

tetanus toxoids (DTaP).


Legionella pneumophila

DiseasesLegionnaires' disease ("atypical" pneumonia).

•Clinical picture vary from mild influenzalike illness to severe pneumonia accompanied by mental confusion, nonbloody diarrhea, proteinuria & microscopic hematuria.•Cough with scanty & nonpurulent sputum. •Most cases resolve spontaneously in 7 to 10 days, but in older or immunocompromised patients, infection can be fatal.•Pontiac fever is mild, flulike form of Legionella infection that does not result in pneumonia.



Characteristics

•Gram-negative rods (stain poorly with standard

Gram stain)•Require iron & cysteine for growth in culture.


•Habitat is environmental water sources.

•Transmission is via aerosol from the water source.

•Person-to-person transmission does not occur.



• It has endotoxin. •Predisposing factors include: - Older than 55 years of age - Smoking damages alveolar macrophages - High alcohol intake. -Immunosuppressed patients (renal transplant recipients)•Organism replicates intracellularly, so cell-mediated immunity is important host defense.

Pathogenesis



•Microscopy with silver impregnation stain or fluorescent antibody. •Culture on charcoal yeast extract agar containing increased amounts of iron & cysteine. •Urinary antigen provides rapid diagnosis.•Serologically by detecting rise in antibody titer in patient's serum.•Hyponatremia (serum sodium ≤ 130 mEq/L) is important laboratory finding that occurs more often in Legionella pneumonia than in pneumonia caused by other bacteria.



Legionella pneumophila growing on GVPC agar Charcoal yeast extract agar

Legionella pneumophila H & E stained lung sections of patient from whom legionella pneumophila was isolated stained with CDC's modification of Dieterle silver impregnation procedure. small, blunt pleomorphic intracellular & extracellular bacilli which stain brown to black against a pale yellow background (500X)



Treatment• Azithromycin or erythromycin.

• Rifampin can be added in severe cases.

No vaccine or prophylactic drug is available.

Prevention

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